DBD::SQLite simply rocks. If you need an extremely fast database-enabled application with very few dependencies this is the ticket. I consider DBD::SQLite in my top-ten list of most useful CPAN distributions. I really can't overstate how useful it can be. With blazing speed, rapid development, stability, and reliability, this distribution has it all.
CPANPLUS gets my vote for "best new module of the year". CPANPLUS is a replacement for the venerable CPAN.pm, and is scheduled for addition in the 5.10 core. CPANPLUS makes installing CPAN modules trivial, and it even supports uninstallation. Developers will appreciate CPANPLUS::Backend, which allows a programatic interface to its functionality. If you are at all serious about perl, this is one must-have module.
HTML::Template is a worthwhile tool for templating, and developing web applications, especially when used in conjunction with CGI::Application. However, since the templating language is light-weight, you may likely run into walls when attempting anything fairly involved (i.e., 'ELSIF' is missing). HTML::Template is useful if your needs are not too great, otherwise you might take a look at HTML::Mason.
Module::Build is a replacement for ExtUtils::MakeMaker, and specifically aims to replace 'make' in the module build process. Module authors should consider using Module::Build instead of EU::MM when creating new distributions. A very solid offering.
POE::Component::IRC is the successor to Net::IRC, and the de facto standard for building IRC-based applications. Its ease-of-use and solid documentation make it the perfect tool for building IRC bots. The author is very open and responsive to feedback. As such, the module is constantly being improved.